Machine assembly

ABSTRACT

A rotatable support for a machine tool having a fixed spindle and a substantially tubular load-receiving member supported concentrically around the spindle with a fluid bearing provided therebetween and having a fluid motor for rotating the loadreceiving member arranged so that its component portions are carried by both the fixed spindle and the load-receiving member whereby upon operating the fluid motor the load-receiving member is rotated in a vibration-free manner. Further, the fluid used to define the fluid bearing provides optimum cooling of the support and its adjoining components.

United States Patent Giardini et al.

[ 1 July 4, 1972 [541 MACHINE ASSEMBLY [72] Inventors: Dante S. Giardini, Kettering; Heinrich J. Wieg, New Burlington, both of Ohio; The Bendix Corporation 22 Filed: Sept.23, 1910 21 Appl.No.: 74,879

Related 1.1.8. Application Data [62] Division of Ser. No. 760,307, Sept. 17, 1968, abancloned.

[521 US. Cl ..51/168, 51/1345 F, 308/122, 91/68 [51] Int. Cl ..B24b 41/00 [58] Field of Search ..51/168, 134.5 F; 308/122; 91/68 [56] References Cited UNITED STATES PATENTS 2,830,541 4/1958 Higgins et al. ..308/122 2,811,109 10/1957 Brill et al. ..308/122 2,147,761 2/1939 Whitecomb ..91/68 734,944 7/1903 Porter ..91/68 3,247,621 4/1966 Aller ..51/l35.5 765,421 7/1904 Fletcher ....51/l35,5 F 3,454,311 7/1969 Tomita et al. ..308/l22 2,459,825 1/1949 Martellotti ..308/l22 3,422,578 1/1969 Mossman et al ..51/168 Primary Examiner-William R. Armstrong Att0rney-Joseph V. Tassone, William F. Thornton and Plante, Hartz, Smith and Thompson [5 7] ABSTRACT A rotatable support for a machine tool having a fixed spindle and a substantially tubular load-receiving member supported concentrically around the spindle with a fluid bearing provided therebetween and having a fluid motor for rotating the load-receiving member arranged so that its component portions are carried by both the fixed spindle and the load-receiving member whereby upon operating the fluid motor the loadreceiving member is rotated in a vibration-free manner. Further, the fluid used to define the fluid bearing provides optimum cooling of the support and its adjoining components.

26 Claims, 10 Drawing Figures PATENTEDJUL] 1972 3.673 743 sum ear 4 VENTORS DANTE GIAR HEINRICH J. WlE

wpai O.

ATTORNEY MACHINE ASSEMBLY CROSS REFERENCE TO RELATED APPLICATION This application is a division of application Ser. No. 760,307 filed Sept. 17, 1968, now abandoned.

BACKGROUND OF THE INVENTION In machine tools such as grinding machines, for example, where varying grinding conditions create high loads and adverse operating conditions it is important that a substantially frictionless rotatable support be provided for the grinding wheel wherein such support provides optimum rigidity, assures operation without excessive temperature buildup, and provides operation in a substantially friction-free manner, whereby the required grinding accuracy is assured. Rotatable supports proposed heretofore are generally inadequate in providing the desired rigidity and hence accuracy of operation or are too expensive to produce and maintain in a satisfactory operating condition over extended periods of use. Further, the supports previously proposed for a grinding wheel are usually electric motor driven through a drive belt and subject the grinding wheel and its associated structural components to undesirable vibrations which tend to reduce the operating efficiency and the precision with which a workpiece may be ground.

SUMMARY This invention provides an improved rotatable support for a machine tool, such as a grinding machine, which is of optimum simplicity, easy to manufacture and maintain, provides optimum performance even under adverse operating conditions, and provides operation in a substantially vibration-free manner by eliminating separate external drive belts or the like.

Other details, uses, and advantages of this invention will become apparent as the following description of the embodiments thereof presented in the accompanying drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show present exemplary embodiments of this invention, in which FIG. 1 is a perspective view of an exemplary grinding machine which has one exemplary embodiment of the rotatable support of this invention provided as an integral part thereof;

FIG. 2 is a cross-sectional view taken essentially on the line 22 of FIG. 1 and particularly illustrating a non-rotatable member or spindle and an associated load-receiving member or housing supported for rotation about such spindle with a precision fluid bearing provided therebetween;

FIG. 3 is a cross-sectional view taken on the line 33 of FIG. 2 and particularly illustrating elements of a fluid motor utilized to drive the load-receiving member about the spindle;

FIG. 4 is a cross-sectional view taken on the line 4-4 of FIG. 2 and particularly illustrating a plurality of four fluid pressure pads and their associated supply orifices defined between the nonrotatable spindle and the rotatable loadreceiving member;

FIG. 5 is a greatly enlarged fragmentary cross-sectional view of the rear end portion of the spindle and rotatable loadreceiving member illustrated in FIG. 2 and particularly illustrating the manner of supplying fluid from an associated fluid supply source to the fluid motor and to the fluid supply lines leading to the pressure pads;

FIG. 6 is a view similar to FIG. 2 illustrating another exemplary embodiment of this invention which utilizes a plurality of six pressure pads between its spindle and associated loadreceiving member and also illustrating a portion of the spindle in elevation;

FIG. 7 is a view similar to FIG. 3 taken on the line 7-7 of FIG. 6 and particularly illustrating another embodiment of a fluid motor which is in the form of a gear motor having only three spur gears;

FIG. 8 is a view similar to FIG. 4 and taken on the line 8-8 of FIG. 6;

FIG. 9 is a perspective view illustrating the nonrotatable spindle of FIG. 2; and

FIG. 10 is a schematic view illustrating an exemplary external fluid system which utilizes a single fluid pump to supply fluid under pressure to both the fluid pressure pads and fluid motor and such fluid system may be utilized with either the spindle of FIG. 2 or the spindle of FIG. 6.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS Reference is now made to FIG. 1 of the drawings which illustrates a machine tool, shown as a grinder 20, which utilizes one exemplary embodiment of the rotatable support of this invention. The grinder has a base 21 which includes a longitudinal way 22 and the longitudinal way 22 supports a headstock 23 and a tailstock 24 for movement therealong in a known manner. Any suitable means of known construction may be provided to adjustably position and fasten the headstock 23 and tailstock 24 along the way 22 and the headstock 23 and tailstock 24 include centers 25 and 26 respectively for carrying a workpiece 27 which is to be ground by the grinder 20.

The grinder 20 has a wheelhead assembly 32 which carries a rotatable support designated generally by a reference numeral 33 for movement toward and away from the workpiece 27 and the support 33 has a grinding wheel 34 fixed thereon so that upon rotating the support 33 and moving it and hence the grinding wheel 34 toward and against the workpiece 27, a precisely ground surface is provided in the workpiece 27 having a contour corresponding to the contour indicated at 35 defined in the outer periphery of the grinding wheel 34. Any suitable means may be utilized to move the wheelhead assembly 32 back and forth on the base 21 and toward and away from the workpiece 27 and such movement may be controlled by a precision hydraulic system at feed rates varying from 0.005 inch to 0.500 inch per minute, for example.

The rotatable support of this invention comprises a nonrotatable member or spindle 36 having a rear mounting flange 37 which is fixed to an outer supporting housing 40comprising the wheelhead assembly 32 by a plurality of bolts 41, see FIG. 2. The outer portion of the spindle 36 has a substantially frustoconical male surface 42 which is adapted to be received tightly within a cooperating frustoconical female surface 43 of a supporting bushing 44 which is suitably fixed to a plate 45 comprising the outer supporting housing 40 of the wheel head assembly 32. The plate 45 may be in the fonn of a hinged access door to enable easy access to the rotatable support 33 of this invention and the grinding wheel 34 carried thereby.

The rotatable support 33 comprises a rotatable load-receiving member shown as a substantially tubular housing member 46 which may have a tubular sleeve 49 fixed thereto and the sleeve 49 of this example has a substantially right circular cylindrical smooth surface 50 defining its inside surface and hence the inside surface of the load-receiving member 46. The grinding wheel 34 is suitably fixed to an adapter 51 by being clamped between an outwardly extending leg portion 52 of such adapter and an annular ring 53 which is fastened against the main portion of the adapter 51 by a plurality of bolts 54 utilized to sandwich and clamp the outer oppositely arranged end surfaces of the grinding wheel between leg portion 52 and annular ring 53. The adapter 51 has a substantially frustoconical surface 55 which is urged against a cooperating frustoconical surface portion 56 of the load-receiving member 46 and the adapter 51 is held in position on the rotatable member 46 by an outer fastening flange 60 which has a plurality of bolts 61 each extending through an associated opening in the flange 60 and through a cooperating threaded opening 62 in the member 46. The fastening member 60 has an axial opening 63 which is adapted to receive the outer end portion of the nonrotating, i.e., dead shaft spindle 36 therethrough.

The nonrotatable member or spindle 36 has a central axis 65 extending longitudinally therethrough and the rotatable load-receiving member 46 with its associated components fixed thereto are symmetrically arranged about the axis 65 of the spindle 36. Fluid bearing means is provided for supporting the member 46 for rotation concentrically about the spindle 36 and in a precision substantially frictionless manner.

Drive means in the form of a fluid, i.e., hydraulic, motor designated generally by the reference numeral 66-is provided for rotating the member 46 and the components carried thereby in a substantially vibration-free manner about the spindle 36 and such vibration-free rotation is achieved by providing the cooperating elements of the fluid motor 66 as component portions of both the nonrotatable spindle 36 and the rotatable member 46, in a symmetrical manner about the longitudinal axis 65 of the spindle 36, and in a manner to be described in detail subsequently in this specification.

A precision fluid bearing is provided between the load receiving member 46 and the spindle 36 and in particular such fluid bearing is defined by a plurality of fluid pressure pads provided between the fixed substantially integral sleeve 49 and cooperating outside surface means of the spindle 36. As seen particularly in FIGS. 2, 4, and 9 of the drawings a plurality of cutouts are provided in one of the membersand such cutouts could be either in the spindle 36' or the load-receiving member 46. It will be appreciated that sleeve 49 is considered as being an integral part of member 46 for all practical purposes.

In this example of the invention the cutouts are each designated by the reference numeral 70 and are provided on substantially the full length of the spindle 36. The cutouts 70 are in the form of symmetrically arranged flats formed in the peripheral surface of the spindle 36 in any suitable manner and the cutouts 70 define pressure pads which will also be designated by the reference numeral 70; thus, the reference numeral 70 will be used when referring to either the pressure pads 70 or the cutouts 70.

In this exemplary embodiment of the invention a plurality of four pressure pads 70 are provided and as previously mentioned the pressure pads 70 extend substantially along the full length of the spindle 36 and supply means is provided for supplying a fluid, such as a suitable oil, from a fluid source shown as a reservoir 73 containing such hydraulic oil to the pressure pads 70. The supply means includes a hydraulic pump 74, see FIG. 2, driven by an electric motor 75. The pump 74 has an inlet in flow communication with the oil in the reservoir 73 and an outlet is suitably connected to a supply line or conduit 76. The conduit 76 has a discharge end portion threadedly fastened to the rear end portion of the spindle 36 as shown at 80.

As best seen in FIG. 5, an internal passage 81 extends through the rear end portion of the spindle 36 and places the discharge end of the conduit 76 in fluid flow communication with an annular chamber 82. A plurality of internal passages 83 extend from the annular chamber 82, see FIGS. 2-5, and each passage 83 terminates in a calibrated orifice 84 which introduces oil in an associated pressure pad 70 in a controlled manner. The passages 83 are similar and are constructed and arranged so that the oil flowing through each passage 83 and through its associated orifice 84 encounters essentially the same resistance to fluid flow whereby the effective oil pressures in the four pressure pads 70 are substantially equal.

It will also be appreciated that the orifices 84 may be varied in size as desired for each application. Also, the pump 74 may be a variable displacement pump which may be driven at any desired speed by the motor 75 so that practically any substantially constant fluid pressure and flow condition may be provided.

Return means is provided for returning the fluid, i.e., oil in this application, from the pressure pads 70 and through the nonrotatable member or spindle 36 to the fluid source or reservoir 73. The oil is returned from the pressure pads 70 through a plurality of radially inwardly directed passages 85 to a comparatively large diameter passage 86 extending substantially centrally through the spindle 46. The internal passage 86 is provided with its discharge end portion 87 arranged adjacent the terminal inner end of the spindle 36 and in flow communication with a return conduit 90 which has an inletportionthreadedly fastened to the spindle 36 as shown at 91. The conduit 90 has its discharge end portion in flow communication with the oil reservoir 73 and returns the oil to such reservoir which has previously flowed through the pressure pads 70.

Each internal passage 83 with an associated orifice 84 at its terminal discharge end is arranged so that such orifice discharges fluid under pressure substantially in the central portion of an associated pressure pad 70, see F IG. 9. The oil from each pressure pad 70 flows essentially in opposite directions from the central portion of each pad 70 and as indicated by the arrows at 93 and 94, flows radially inwardly through the passages 85, and then flows toward the reservoir 73 through the longitudinal passage 86 in the spindle 36.

To assure that the oil supplied from the reservoir 73 to the pressure pads 70 does not leak or seep from the support 33, a pair of seals, formed in this example as lip seals, is provided to associate with opposite ends of the spindle 36. An outer lip seal 95 is provided adjacent the outer end of the spindle 36 and is supported in a known manner in an annular supporting member 96 of U-shaped cross-sectional configuration. The member 96 has the inner end portion of the seal 95 suitably fixed in position thereagainst so that the outer portion of the seal engages a reduced diameter right circular cylindrical surface of the spindle 36 as indicated at 100 to provide a fluid seal between the member 46 and spindle 36. Another lip seal 101 is provided adjacent the inner end portion of the spindle 36 and the seal 101 is suitably fastened in an annular supporting member 102 also of substantially U-shaped cross-sectional configuration. The seal 101 has its inner end portion suitably fixed to the member 102 and its outer annular surface engages a reduced diameter right circular cylindrical inner end portion of the spindle 36 as indicated at 103.

Thus, it will be appreciated that oil under pressure is provided by the pump 74 through conduit 76, annular chamber 82, and internal passages 83 to the pressure pads 70 and such oil is provided at a controlled high pressure so as to provide a controlled laminar flow in the pressure pads 70. The oil is then returned to the central passage 86 in the spindle 36 and back to the reservoir 73 through the return conduit 90. From this configuration it will be appreciated that oil under controlled pressure is constantly circulated around and through the fixed spindle 36 and against the inside cylindrical surface of the integral sleeve 49 defining the rotatable load-receivable member 46 whereby not only is there a precision frictionless fluid bearing defined by the pressure pads 70 between the spindle 36 and the loadreceiving member 46 but also the supply means and return means assure cool operation of the rotatable support assembly 33 of this invention under all operating conditions including adverse high load conditions. It will also be appreciated that by recirculating the oil in the manner illustrated and described the support assembly 33 may be operated at a substantially uniform temperature whereby the rigidity of the support remains substantially constant and precision grinding may be obtained under practically all load conditions.

As previously mentioned, the rotatable support 33 of this invention is driven by fluid motor 66 which has cooperating elements comprising portions of both the nonrotatable spindle 36 and the rotatable load-receiving member 46 whereby the loadreceiving member 46 and the associated structural members carried thereby, including the grinding wheel 34, may be rotated in a substantially vibration-free manner and as will now be described in detail and by referring particularly to FIGS. 2, 3 and 5 of the drawings.

The cooperating elements of the hydraulic motor 66 are symmetrically arranged about the central longitudinal axis 65 of the spindle 36 and in this example of the invention comprise a plurality of substantially identical spur gears each designated by the reference numeral 105 and each being supported for rotation about an associated central shaft 106 which is carried by the spindle 36. Each spur gear 105 has a plurality of gear teeth 110 which engage a rotatable annular member shown as a ring gear 111 which is suitably fixed to the rotatable loadreceiving member 46. The ring gear 111 has a plurality of radially inwardly projecting gear teeth 112 which are adapted to be engaged by the teeth 1 of the spur gears 105 and the spur gears 105 are rotated by fluid under pressure from a suitable fluid source and in a manner to be described subsequently.

As the spur gears 105 are rotated by fluid under pressure they rotate about their associated shafts 106 and because the teeth 1 10 are in cooperating engagement with the teeth 1 12 of the ring gear 111 rotation of the spur gears 105 causes the ring gear 111 to be rotated to thereby simultaneously rotate the load-receiving member 46, inasmuch as the ring gear 111 is fixed to the member 46. The spur gears 105 and ring gear 111 comprise component members of an epicyclic gear train wherein the epicyclic gear train is symmetrically arranged about the axis 65 and helps provide the substantially vibrationfree operation mentioned earlier.

The fluid under pressure utilized to drive the fluid motor 66 may be provided from any suitable source and may be completely independent from the fluid utilized to define the fluid bearing between the spindle 36 and the rotatable member 46. However, in this exemplary embodiment of the invention the fluid is preferably the oil provided in reservoir 73 and which is utilized to define the fluid bearing system previously described in detail and such oil is provided to the support 33 through a conduit 1 13.

A separate pump 114 is provided and driven by an electric motor 1 and the pump 114 has its inlet in flow communication with the oil in the reservoir 73 and its discharge in flow communication with the conduit 1 13. The pump 114 may be a variable displacement pump which may be adjustably controlled manually or may be controlled by any suitable automatic means and the speed of rotation of the motor may also be suitably controlled, whereby the pressure and rate of flow of the fluid supplied to the fluid motor 66 may be controlled in a precise manner.

The conduit 113 has its discharge end threadedly fastened to the spindle 36 as indicated at 120, see FIG. 5, and an internal passage 121 is provided in the rear end portion of the spindle 36 and arranged so that its inlet end is in fluid flow communication with the discharge end of the conduit 113 and the discharge end of the passage 121 is in fluid flow communication with an annular chamber 122, which is similar to the chamber 82. A plurality of passages 123 are provided in the spindle 36, see FIGS. 3 and 5, and each passage 123 is arranged in flow communication with the chamber 122 and with an associated spur gear element 105 so that upon supplying fluid under pressure through each passage 123 from annular chamber 122 the gear elements 105 are rotated by the oil under pressure provided by pump 114 and in a known manner.

An outer discharge passage 125 is provided for association with each spur gear 105 and each passage 125 has its inlet arranged downstream of an associated inlet or supply passage 123 for its associated spur gear or gear element 105. Each passage 125 has a discharge end 126 arranged so that fluid under pressure utilized to drive its associated spur gear 105 may be returned to the reservoir 73.

Although a separate fluid system could be utilized in the support 33 to return the oil used to drive the fluid motor 66, in this exemplary embodiment of the invention the oil is returned through the radially inwardly extending passages 85 provided adjacent the inner end portion of the spindle 36. As previously explained the passages 85 also receive oil from adjacent pressure pads of the fluid system and as indicated by the arrow at 94. The passages 85 are arranged in flow communication with the longitudinal passage 86 utilized to return oil from the pressure pads 70 to the reservoir 73. Thus, it will be appreciated that substantially the same return conduit system is utilized to return the oil utilized to drive the hydraulic motor 66 as is utilized to return the oil which provides the frictionless fluid bearing between the spindle 36 and rotatable load-receiving member 46.

As previously explained the pump 114 may be a variable displacement pump and the speed of its driving motor may also be adjustably controlled whereby the rotatable loadreceiving member 46 and hence the grinding wheel 34 carried thereby may be driven in any desired manner and as a function of the load which is applied against the grinding wheel 34.

Thus, not only does the construction and arrangement of the drive motor 66 in the support 33 provide the substantially vibration-free operation previously described but also enables control of the operation of the grinding wheel 34 as a function of loading of such grinding wheel to thereby assure maximum operating efficiency. It will also be appreciated that any suitable servo valve means, or the like, may be utilized to automatically control the operation of the fluid or hydraulic motor 66 in direct proportion to the load being applied against the grinding wheel 34 and this offers optimum versatility for the rotatable support of this invention not only when applied to a grinder but also in any machine tool application where it is desired to control the operation of a cutting tool as a function of load.

As seen particularly in FIGS. Sand 9 of the drawings a plurality of recess means each designated by the reference numeral 131 are provided in integral annular portions comprising the rear of the nonrotating spindle 36. Each recess means 131 is in the form of a groove, the open portion of which faces an associated annular surface of the rotatable ring gear 111 and each recess means 131 is adapted to receive oil under pressure from a suitable fluid source. The recess means 131 define what may also be considered as fluid balance pads, or the like. The recess means or balance pads 131 function in a similar manner as the pressure pads 70. However, the construction and arrangement of the fluid pads 131 is such that they operate to define and serve as a precision self-adjusting axial thrust bearing for the support 33. In particular, it will be seen that the pressure pads 131 precisely position the ring gear 111, because they act against opposed surfaces thereof, which also precisely positions the rotatable load-receiving member 46 and all of the members carried by the member 46 including the grinding wheel 34.

As previously mentioned, the recess means or fluid balance pads 131 may be provided with oil under pressure from any suitable source. However, in this example of the invention, each pad 131 is provided with oil under pressure through a line 129 from an associated passage 83 used to provide oil to a particular fluid pressure pad 70. It will also be appreciated that, if desired, the oil to the balance pads 131 may be provided through associated passages suitably interconnected to the passage 121 which provides oil under pressure to the fluid motor 66.

In many devices proposed heretofore a rotatable loadreceiving member similar to member 46 would normally be driven by an externally arranged drive such as a drive motor driving a drive belt, for-example, which engages one end of the rotatable member and imposes a load transverse to the longitudinal axis of the load-receiving member. Inherently such an arrangement introduces excessive vibration and limits the versatility of each previously proposed device.

By contrast, the unique construction of the rotatable support 33 with its frictionless fluid bearing system and integral hydraulic drive motor 66 enables the entire support 33 to be provided on a versatile assembly such as a swivel assembly, for example, so that the grinding wheel 34 may be fed toward the workpiece 27 at any desired adjustable angle. Also, the simple and economical construction of the rotatable support 33 provides the substantially vibration-free operation previously described, the inherent ability to take care of axial thrust loads, and an improved integral fluid bearing system.

Another exemplary embodiment of this invention is illustrated in FIGS. 6-8 of the drawings. The rotatable support of FIGS. 6-8 is very similar to the support 33; therefore, such support will be designated generally be the reference numeral 33A and parts of the support 33A which are very similar to corresponding parts of support 33 will be designated by the same numeral as in support 33, also followed by the letter designation A and not described again. Only those component parts of the support 33A which are substantially different from corresponding parts of the support 33 will be designated by new reference numerals also followed by the letter designation A and described in detail. The support 33A of FIGS. 6-8 may be utilized in the wheelhead assembly of the grinder in a similar manner as the support 33. I

For those parts of the support 33A and associated components which carry the same reference numerals, followed by the letter designation A, as in the support 33, the previous description is fully applicable and reference may again be made to the previous description, as desired.

The main differences between the rotatable support 33A and the support 33 are'in the construction and arrangement of the nonrotatable member or spindle, which will be designated by the reference numeral 136A in the support 33A. Also, the fluid motor is different in the support 33A and is designated generally by the reference numeral 140A. The detailed description will proceed with a discussion of the fluid or hydraulic motor 140A, followed by a detailed description of the spindle 136A.

The fluid motor 140A instead of having a plurality of four rotatable elements or spur gears 105A cooperating with an associated ring gear 111A fixed to a support 46A only has a plurality of three spur gears 105A. The spur gears 105A are supplied with fluid or oil from their associated passages 123A and the oil is discharged from the gears 105A into return passages 125A and in a similar manner as previously described in detail in connection with similar passages 125 in the previous embodiment of this invention.

The spindle 136A of this exemplary embodiment of the invention has a plurality of six cutouts 70A which define pressure pads also designated by the reference numeral 70A in a similar manner as previously described in connection with the pressure pads 70 of the rotatable support 33. The cutouts 70A and hence pressure pads 70A in the spindle 136A are symmetrically-arranged'with respect to the central axis 65A through such spindle and the cutouts are arranged in a plurality of sets with each set having at least two spaced cutouts, i.e., pressure pads, 70A arranged in aligned end-to-end relation roughly parallel to the central axis 65A- Thus, it will be seen that the pressure pads 70A of this example define a plurality of three sets spaced 120 degrees apart with two pads 70A in each set, whereby a total of six fluid pressure pads 70A are defined. However, it will be appreciated that any desired number of pressure pads 70A may be provided for association with the spindle 136A as long as such pressure pads 70A are placed in a symmetrical pattern about the central axis 65A of the spindle 136A. Further, it will be appreciated that the pressure pads 70A may have any desired effective fluid area as determined by the particular application of the support 33A.

The cutouts 70A and hence the pressure pads 70A defined thereby may be provided in the spindle 136A by any suitable technique such as by integrally casting such cutouts or recesses in the spindle 136A or such cutouts may be provided by machining or other suitable material removing process.

The oil from each of the pressure pads 70A is returned to the reservoir 73A through a central passage 86A in the spindle 136A and then through a return line 90A in a similar manner as previously described in detail in connection with corresponding components of the support 33. The oil from each pad 70A may be conveyed to the central passage 86A in any suitable manner; however, in this example of the invention each pressure pad 70A is arranged in flow communication with associated annular grooves 143A, each having associated radially inwardly extending integral passages 144A and each passage 144A communicates with the central passage 86A.

It will also be appreciated that each internal passage 83A has a passage 89A extending therefrom and arranged in flow communication with an associated orifice 84A. The passages 89A are sized to take into account the pressure drops in the fluid system and to assure the pressure of the oil in each pad A is at a substantially constant level to thereby assure that the overall fluid bearing provided between the spindle 136A and the sleeve insert 49A comprising an integral part of the load-receiving member 46A provides the desired optimum performance.

Each of the rotatable supports 33 and 33A of this invention with its frictionless fluid bearing and integral fluid motor in each instance provides an assembly which together with its associated fluid lines operates essentially full of oil under all normal operating conditions. It has been found by test that operating the rotatable support full of oil tends to provide a better dynamic balance at practically all operating speeds. Further, with the support assembly operating full of recirculating oil there is more uniform temperature distribution throughout the entire support and it is easier to hold manufacturing tolerances, such as grinding tolerances in this exemplary grinder application.

Any suitable fluid may be utilized for both the fluid motor system and forthe fluid bearing system comprising each of the rotatable supports 33 and 33A of this invention and SAE 20W oil has been successfully utilized. In the case of the fluid motor system it has been found that a pump operating at roughly 400 pounds per square inch pressure and capable of delivering 20 gallons per minute provides rotational speeds of the associated rotatable member 46 or 46A generally of the order of 1,500 revolutions per minute. However, as previously indicated the pump in each instance may be of the type which is capable of providing an adjustable flow and pressure whereby rotation of the associated member 46 or 46A may be varied depending upon load conditions. Also, the fluid pressure in the fluid bearing system will be determined in each instance by the load conditions to be imposed on the rotatable member 46 or 46A and such pressure may be adjusted as previously described.

Another exemplary embodiment of this invention is illustrated in FIG. 10 of the drawings wherein a schematic view is presented which illustrates an exemplary external fluid system which may be utilized in association with either the rotatable supports 33 or 33A presented in this specification. The main feature of the external fluid system illustrated in FIG. 10 is that it utilizes a single fluid pump.

The fluid system presented in FIG. 10 utilizes a number of components which may be similar to components previously described in connection with the rotatable supports 33 and 33A and components of the fluid system of FIG. 10 which are very similar to corresponding components of either the rotatable support 33 or 33A will carry the same reference numeral as in previous presentations followed by theletter designation M. Only those component portions which are substantially different from component portions discussed previously will be designated by a new reference numeral also followed by the letter designation M and described in detail. The manner in which the schematic presentation of FIG. 10 is presented will enable an easy understanding of how the system of FIG. 10 may be utilized in either of the rotatable supports previously described.

In particular, it will be seen that the system of FIG. 10 has a reservoir 73M and that oil is returned to the reservoir through a single return line M which is arranged in fluid flow communication with internal passage 86M to return oil from both the fluid pressure pads and the integral hydraulic motor. A single hydraulic pump M is provided and driven by an electric motor 151M and the pump 150M has its inlet in fluid flow communication with the oil in the reservoir 73M and its discharge end connected to an external conduit 152M which has a tee connection 153M at its terminal end.

One leg of the tee connection 153M is arranged in fluid flow communication with a conduit 76M which in turn communicates with an internal passage 81M which supplies oil to the pressure pads and the other leg of the tee connection 153M is arranged in fluid flow communication with a conduit 113M which in turn is arranged in flow communication with internal passage 121M which supplies oil to the fluid motor. Thus, it is seen that a single pump 150M and conduit 152M supply fluid passages 81M and 121M to the pressure pads and integral fluid motor respectively.

The external fluid system presented in FIG. with its single pump 150M supplying both the spindle pressure pads and the integral fluid motor driving the rotatable support around the fixed spindle provide, in effect, a load compensating spindle. In particular, the operation of the system of FIG. 10 is such that as the grinding wheel load increases the hydraulic drive oil pressure also increases which in turn increases oil bearing support pressure and compensates for the additional load imposed on the grinding wheel.

While present exemplary embodiments of this invention have been illustrated and described, it will be recognized that this invention may be otherwise variously embodied and practiced within the scope of the following claims.

. We claim:

1. A grinder comprising, a nonrotatable member having a central longitudinal axis, a rotatable load-receiving member having an opening which receives said nonrotatable member therethrough and having exposed easily accessible support means, a grinding wheel detachably fixed on said support means for rotation with said rotatable member, a plurality of cutouts in one of said members defining a corresponding plurality of fluid pressure pads, supply means for supplying a fluid from a fluid source to said plurality of pressure pads to maintain the fluid in said pressure pads at a substantially constant pressure while providing continuous fluid flow therethrough, return means for returning said fluid from said pressure pads through said nonrotatable member and to said fluid source, and drive means for rotating said rotatable member together with said grinding wheel, said fluid pressure pads providing a precision fluid bearing enabling said rotatable member and grinding wheel to be rotated in a substantially frictionless manner while said supply means and return means assure said fluid is circulated to provide cool operation of said members even during adverse grinding conditions.

2. A grinder as set forth in claim 1 in which said nonrotatable member comprises a fixed spindle, said support means comprises exposed easily accessible support means, and said supply means and return means comprise passages extending longitudinally through said spindle.

3. A machine tool comprising, a nonrotatable member having a central longitudinal axis, a rotatable load-receiving member having an opening which receives said nonrotatable member therethrough and having exposed easily accessible support means, a machining instrument detachably fixed on said support means for rotation with said rotatable member, a plurality of cutouts in one of said members defining a corresponding plurality of fluid pressure pads, supply means for supplying a fluid from a fluid source longitudinally through said nonrotatable member and to said plurality of pressure pads to maintain the fluid in said pressure pads at a substantially constant pressure while providing continuous fluid flow therethrough, return means for returning said fluid from said pressure pads longitudinally through said nonrotatable member and to said fluid source, and drive means for rotating said rotatable member together with said machining instrument, said fluid pressure pads providing a precision fluid bearing enabling said rotatable member and machining instrument to be rotated in a substantially frictionless manner while said supply means and return means assure said fluid is circulated to provide cool operation of said members even during adverse machining conditions.

4. A machine tool as set forth in claim 3 in which said drive means comprises a fluid motor having its cooperating elements provided as component parts of both said nonrotatable member and said rotatable member and in a symmetrical manner about said central longitudinal axis to thereby provide substantially vibration-free rotation of said rotatable member.

5. A machine tool as set forth in claim 4 and further comprising an adjustable pump having its inlet in flow communication with said fluid source and its outlet in flow communication with said fluid motor to enable controlling the fluid supplied to said fluid motor and hence rotation of said rotatable member.

6. A machine tool as set forth in claim 4 in which said nonrotatable member has opposed recess means provided therein in integral annular portions comprising the rear portion thereof each recess means defining a fluid balance pad and being arranged to face an associated surface means comprising said rotatable member, and said balance pads being provided with fluid under pressure and cooperate to define a precision self-adjusting axial thrust bearing for said rotatable support.

7. A machine tool as set forth in claim 3 in which said plurality of pressure pads in said one member extend substantially along the full axial length thereof and are symmetrically arranged relative to said central axis, and said supply means comprises a plurality of internal passages extending longitudinally through said nonrotatable member from one end portion thereof with each internal passage terminating in a discharge orifice which exits fluid in the central portion of an associated pressure pad.

8. A machine tool as set forth in claim 3 provided in the form of a grinder wherein said easily accessible support means supports a machining instrument in the form of a grinding wheel and said cutouts are provided in the form of symmetrically arranged flats formed in the peripheral surface of said nonrotatable member.

9. A machine tool as set forth in claim 3 in which said plurality of pressure pads in said one member are symmetrically arranged relative to said central axis and are arranged in a plurality of sets with each set having at least two spaced pressure pads arranged in aligned end-to-end relation roughly parallel to said central axis.

10. A machine tool as set forth in claim 9 in which said nonrotatable member comprises a fixed spindle for said machine tool and said cutouts defining said pressure pads extend inwardly from the peripheral surface of said spindle.

1 l. A machine tool as set forth in claim 3 in which said drive means comprises a fluid motor, said motor having a plurality of rotatable driving elements supported for rotation on said nonrotatable member and arranged in a symmetrical manner about the central longitudinal axis thereof and a rotatable annular element symmetrically arranged around said plurality of rotatable elements and being fixed to said rotatable member, said annular element being driven by said plurality of rotatable driving elements to thereby simultaneously drive said rotatable member in a substantially vibration-free manner.

12. A machine tool as set forth in claim 11 in which said plurality of rotatable elements are driven by fluid under pressure supplied from said fluid source and further comprising adjustable pump means for controlling the pressure of said fluid to said plurality of rotatable elements.

13. A machine tool as set forth in claim 1 1 in which said plurality of rotatable driving elements comprise a plurality of spur gears of an epicyclic gear train, said annular element comprises a ring gear of said epicyclic gear train fixed to said rotatable member and having radially inwardly projecting gear teeth adapted to be engaged by the teeth of said spur gears to thereby rotate said ring gear and said rotatable member, and further comprising opposed recess means provided in said nonrotatable member, each recess means defining a fluid balance pad and being arranged to face an associated surface of said ring gear, said balance pads being provided with fluid under pressure and cooperating to define a precision self-adjusting axial thrust bearing for said rotatable member.

14. A machine tool as set forth in claim 13 and further comprising a chamber provided in said nonrotatable member adjacent one end thereof, said chamber being supplied with said fluid under pressure provided to operate said fluid motor, an individual supply passage from said chamber to each associated rotatable driving element of said plurality of rotatable driving elements, and an individual discharge passage from each rotatable element to said fluid return means from said fluid pressure pads.

15. A machine tool comprising, a fixed spindle having a central longitudinal axis, a rotatable load-receiving member having an opening which receives said spindle therethrough and having exposed easily accessible support means, a machining instrument detachably-fixed on said support means for rotation with said rotatable member, a plurality of cutouts in said spindle defining a corresponding plurality of fluid pressure pads, a reservoir containing hydraulic fluid, supply means for supplying fluid from said reservoir through said spindle to said plurality of pressure pads to maintain the fluid in said pressure pads at a substantially constant pressure while providing continuous fluid flow therethrough, return means for returning said fluid from said pressure pads through said spindle to said reservoir, and drive means provided for rotating said rotatable member together with said machining instrument on said spindle, said fluid pressure pads providing a precision fluid bearing enabling said rotatable member and machining instrument to be rotated in a substantially frictionless manner about said spindle while said supply means and return means assure said fluid is circulated to provide cool operation of said spindle and rotatable member even under adverse machining conditions.

16. A machine tool as set forth in claim 15 in which said drive means comprises a fluid motor having its cooperating elements provided as component parts of both said rotatable member and said spindle and in a symmetrical manner about said central longitudinal axis to thereby provide substantially vibration-free rotation of said rotatable member, said spindle has opposed recess means provided therein, each recess means defining a fluid balance pad and being arranged to face an associated surface means comprising said rotatable member, and said balance pads being provided with fluid under pressure and cooperate to define a precision self-adjusting axial thrust bearing for said rotatable member.

17. A machine tool as set forth in claim 15 in which said plurality of pressure pads in said spindle extend substantially along the full axial length thereof and are symmetrically arranged relative to said central axis, said supply means comprises a plurality of internal passages extending through said spindle with each internal passage terminating in a discharge orifice which exits fluid in the central portion of an associated pressure pad, and said return means comprises a passage extending longitudinally through said spindle and a plurality of radial passages each extending from said longitudinal passage and in flow communication with an associated pressure pad.

18. A machine tool as set forth in claim 15 in which said plurality of pressure pads in said spindle are symmetrically arranged relative to said central axis and are arranged in a plurality of sets with each set having at least two spaced pressure pads arranged in aligned end-to-end relation roughly parallel to said central axis, said supply means comprises a plurality of internal passages extending through said spindle with each internal passage terminating in a discharge orifice which exits fluid in the central portion of an associated pressure pad, and said return means comprises a passage extending longitudinally through said spindle and a plurality of radial passages each extending from said longitudinal passage and provided in flow communication with an associated pressure pad.

19. A machine tool as set forth in claim 18 in which said supply means further comprises an annular chamber provided in said spindle adjacent one end thereof, said chamber serving as a supply manifold for said plurality of internal passages.

20. A machine tool as set forth in claim 15 in which said drive means comprises a fluid motor, said motor having a plurality of rotatable elements supported for rotation on said spindle and arranged in a symmetrical manner about the central longitudinal axis thereof and a rotatable annular element symmetrically arranged around said plurality of rotatable elements and being fixed to said rotatable member, said annular element being arranged within the peripheral outline of said rotatable member and being driven by said plurality of rotatable elements to thereby provide a compact construction and simultaneously drive said rotatable member in a substantially vibration-free manner.

21. A machine tool as set forth in claim 20 and further comprising a chamber provided in said spindle, said chamber being connected to a source of pressurized operating fluid for said fluid motor, and an individual passage from said chamber to each associated rotatable element of said plurality of rotatable elements.

22. A machine tool as set forth in claim 21 in which said plurality of rotatable elements comprise a plurality of spur gears of an epicyclic gear train and said annular element comprises a ring gear of said epicyclic gear train having radially inwardly.

projecting gear teeth adapted to be engaged by the teeth of said spur gears to thereby rotate said ring gear and said rotata ble member.

23. A machine tool comprising, a nonrotatable member having a central longitudinal axis, a rotatable load-receiving member having an opening which receives said nonrotatable member therethrough and having exposed easily accessible support means, a machining instrument detachably fixed on said support means for rotation with said rotatable member, a plurality of cutouts in one of said members defining a corresponding plurality of fluid pressure pads, a reservoir containing hydraulic fluid, first supply means for supplying and continuously flowing fluid under pressure from said reservoir through said nonrotatable member and through said plurality of pressure pads, first return means for returning said fluid from said pressure pads longitudinally through said nonrotatable member and to said reservoir, a fluid motor for rotating said rotatable member together with said machining instrument, said fluid motor having its cooperating elements provided as component parts of both said nonrotatable member and said rotatable member and in a summetrical manner about said central longitudinal axis to thereby provide sub stantially vibration-free rotation of said rotatable member and said machining instrument, second supply means for supplying fluid under pressure from said reservoir to said fluid motor, second return means for flowing fluid from said fluid motor into said first return means for return to said reservoir, and pressurizing means for pressurizing and supplying fluid from said reservoir to both said first supply means and said second supply means, said fluid pressure pads providing a precision fluid bearing enabling said rotatable member and said machining instrument to be rotated in a substantially frictionless manner with said fluid being circulated by said pressurizing means to provide cool operation of said members even under adverse machining conditions.

24. A machine tool as set forth in claim 23 in which said pressurizing means comprises a single fluid pump having its inlet in fluid flow communication with said fluid in said reservoir and its outlet in fluid flow communication with both said first and second supply means to thereby supply both said fluid pressure pads and said integral fluid motor, said fluid pump comprising a load-compensating system wherein as the load exerted on said machining instrument increases the fluid pressure provided by said pump to said fluid motor increases which also increases the fluid pressure to said pressure pads thus compensating for the additional load imposed on the machining instrument.

25. A machine tool as set forth in claim 23 in which said pressurizing means comprises a first fluid pump having its inlet in fluid flow communication with said fluid in said reservoir and its outlet in fluid flow communication with said first supply means, and a second fluid pump having its inlet in fluid flow communication with said fluid in said reservoir and its outlet in fluid flow communication with said second supply means.

26. A machine tool as set forth in claim 23 in which said fluid motor comprises a plurality of spur gears of an epicyclic gear train supported for rotation on said nonrotatable member and a ring gear of said epicyclic gear train fixed to said rotatable member and having radially inwardly projecting gear teeth sociated surface of said ring gear, said balance pads being provided with fluid under pressure and cooperating to define a precision self-adjusting axial thrust bearing for said rotatable member. 

1. A grinder comprising, a nonrotatable member having a central longitudinal axis, a rotatable load-receiving member having an opening which receives said nonrotatable member therethrough and having exposed easily accessible support means, a grinding wheel detachably fixed on said support means for rotation with said rotatable member, a plurality of cutouts in one of said members defining a corresponding plurality of fluid pressure pads, supply means for supplying a fluid from a fluid source to said plurality of pressure pads to maintain the fluid in said pressure pads at a substantially constant pressure while providing continuous fluid flow therethrough, return means for returning said fluid from said pressure pads through said nonrotatable member and to said fluid source, and drive means for rotating said rotatable member together with said grinding wheel, said fluid pressure pads providing a precision fluid bearing enabling said rotatable member and grinding wheel to be rotated in a substantially frictionless manner while said supply means and return means assure said fluid is circulated to provide cool operation of said members even during adverse grinding conditions.
 2. A grinder as set forth in claim 1 in which said nonrotatable member comprises a fixed spindle, said support means comprises exposed easily accessible support means, and said supply means and return means comprise passages extending longitudinally through said spindle.
 3. A machine tool comprising, a nonrotatable member having a central longitudinal axis, a rotatable load-receiving member having an opening which receives said nonrotatable member therethrough and having exposed easily accessible support means, a machining instrument detachably fixed on said support means for rotation with said rotatable member, a plurality of cutouts in one of said members defining a corresponding plurality of fluid pressure pads, supply means for supplying a fluid from a fluid source longitudinally through said nonrotatable member and to said plurality of pressure pads to maintain the fluid in said pressure pads at a substantially constant pressure while providing continuous fluid flow therethrough, return means for returning said fluid from said pressure pads longitudinally through said nonrotatable member and to said fluid source, and drive means for rotating said rotatable member together with said machining instrument, said fluid pressure pads providing a precision fluid bearing enabling said rotatable member and machining instrument to be rotated in a substantially frictionless manner while said supply means and return means assure said fluid is circulated to provide cool operation of said members even during adverse machining conditions.
 4. A machine tool as set forth in claim 3 in which said drive means comprises a fluid motor having its cooperating elements provided as component parts of both said nonrotatable member and said rotatable member and in a symmetrical manner about said central longitudinal axis to thereby provide substantially vibration-free rotation of said rotatable member.
 5. A machine tool as set forth in claim 4 and further comprising an adjustable pump having its inlet in flow communication with said fluid source and its outlet in flow communication with said fluid motor to enable controlling the fluid supplied to said fluid motor and hence rotation of said rotatable member.
 6. A machine tool as set forth in claim 4 in which said nonrotatable member has opposed recess means provided therein in integral annular portions comprising the rear portion thereof each recess means defining a fluid balance pad and being arranged to face an associated surface means comprising said rotatable member, and said balance pads being provided with fluid under pressure and cooperate to define a precision self-adjusting axial thrust bearing for said rotatable support.
 7. A machine tool as set forth in claim 3 in which said plurality of pressure pads in said one member extend substantially along the full axial length thereof and are symmetrically arranged relative to said central axis, and said supply means comprises a plurality of internal passages extending longitudinally through said nonrotatable member from one end portion thereof with each internal passage terminating in a discharge orifice which exits fluid in the central portion of an associated pressure pad.
 8. A machine tool as set forth in claim 3 provided in the form of a grinder wherein said easily accessible support means supports a machining instrument in the form of a grinding wheel and said cutouts are provided in the form of symmetrically arranged flats formed in the peripheral surface of said nonrotatable member.
 9. A machine tool as set forth in claim 3 in which said plurality of pressure pads in said one member are symmetrically arranged relative to said central axis and are arranged in a plurality of sets with each set having at least two spaced pressure pads arranged in aligned end-to-end relation roughly parallel to said central axis.
 10. A machine tool as set forth in claim 9 in which said nonrotatable member comprises a fixed spindle for said machine tool and said cutouts defining said pressure pads extend inwardly from the peripheral surface of said spindle.
 11. A machine tool as set forth in claim 3 in which said drive means comprises a fluid motor, said motor having a plurality of rotatable driving elements supported for rotation on said nonrotatable member and arranged in a symmetrical manner about the central longitudinal axis thereof and a rotatable annular element symmetrically arranged around said plurality of rotatable elements and being fixed to said rotatable member, said annular element being driven by said plurality of rotatable driving elements to thereby simultaneously drive said rotatable member in a substantially vibration-free manner.
 12. A machine tool as set forth in claim 11 in which said plurality of rotatable elements are driven by fluid under pressure supplied from said fluid source and further comprising adjustable pump means for controlling the pressure of said fluid to said plurality of rotatable elements.
 13. A machine tool as set forth in claim 11 in which said plurality of rotatable driving elements comprise a plurality of spur gears of an epicyclic gear train, said annular element comprises a ring gear of said epicyclic gear train fixed to said rotatable member and having radially inwardly projecting gear teeth adapted to be engaged by the teeth of said spur gears to thereby rotate said ring gear and said rotatable member, and further comprising opposed recess means provided in said nonrotatable member, each recess means defining a fluid balance pad and being arranged to face an associated surface of said ring gear, said balance pads being provided with fluid under pressure and cooperating to define a precision self-adjusting axial thrust bearing for said rotatable member.
 14. A machine tool as set forth in claim 13 and further comprising a chamber provided in said nonrotatable member adjacent one end thereof, said chamber being supplied with said fluid under pressure provided to operate said fluid motor, an individual supply passage from said chamber to each associated rotatable driving element of said plurality of rotatable driving elements, and an individual discharge passage from each rotatable element to said fluid return means from said fluid pressure pads.
 15. A machine tool comprising, a fixed spindle having a central longitudinal axis, a rotatable load-receiving member having an opening which receives said spindle therethrough and having exposed easily accessible support means, a machining instrument detachably fixed on said support means for rotation with said rotatable member, a plurality of cutouts in said spindle defining a corresponding plurality of fluid pressure pads, a reservoir containing hydraulic fluid, supply means for supplying fluid from said reservoir through said spindle to said plurality of pressure pads to maintain the fluid in said pressure pads at a substantially constant pressure while providing continuous fluid flow therethrough, return means for returning said fluid from said pressure pads through said spindle to said reservoir, and drive means provided for rotating said rotatable member together with said machining instrument on said spindle, said fluid pressure pads providing a precision fluid bearing enabling said rotatable member and machining instrument to be rotated in a substantially frictionless manner about said spindle while said supply means and return means assure said fluid is circulated to provide cool operation of said spindle and rotatable member even under adverse machining conditions.
 16. A machine tool as set forth in claim 15 in which said drive means comprises a fluid motor having its cooperating elements provided as component parts of both said rotatable member and said spindle and in a symmetrical manner about said central longitudinal axis to thereby provide substantially vibration-free rotation of said rotatable member, said spindle has opposed recess means provided therein, each recess means defining a fluid balance pad and being arranged to face an associated surface means comprising said rotatable member, and said balance pads being provided with fluid under pressure and cooperate to define a precision self-adjusting axial thrust bearing for said rotatable member.
 17. A machine tool as set forth in claim 15 in which said plurality of pressure pads in said spindle extend substantially along the full axial length thereof and are symmetrically arranged relative to said central axis, said supply means comprises a plurality of internal passages extending through said spindle with each internal passage terminating in a discharge orifice which exits fluid in the central portion of an associated pressure pad, and said return means comprises a passage extending longitudinally through said spindle and a plurality of radial passages each extending from said longitudinal passage and in flow communication with an associated pressure pad.
 18. A machine tool as set forth in claim 15 in which said plurality of pressure pads in said spindle are symmetrically arranged relative to said central axis and are arranged in a plurality of sets with each set having at least two spaced pressure pads arranged in aligned end-to-end relation roughly parallel to said central axis, said supply means comprises a plurality of internal passages extending through said spindle with each internal passage terminating in a discharge orifice which exits fluid in the central portion of an associated pressure pad, and said return means comprises a passage extending longitudinally through said spindle and a plurality of radial passages each extending from said longitudinal passage and provided in flow communication with an associated pressure pad.
 19. A machine tool as set forth in claim 18 in which said supply means further comprises an annular chamber provided in said spindle adjacent one end thereof, said chamber serving as a supply manifold for said plurality of internal passages.
 20. A machine tool as set forth in claim 15 in which said drive means comprises a fluid motor, said motor having a plurality of rotatable elements supported for rotation on said spindle and arranged in a symmetrical manner about the central longitudinal axis thereof and a rotatable annular element symmetrically arranged around said plurality of rotatable elements and being fixed to said rotatable member, said annular element being arranged within the peripheral outline of said rotatable member and being driven by said plurality of rotatable elements to thereby provide a compact construction and simultaneously drive said rotatable member in a substantially vibration-free manner.
 21. A machine tool as set forth in claim 20 and further comprising a chamber provided in said spindle, said chamber being connected to a souRce of pressurized operating fluid for said fluid motor, and an individual passage from said chamber to each associated rotatable element of said plurality of rotatable elements.
 22. A machine tool as set forth in claim 21 in which said plurality of rotatable elements comprise a plurality of spur gears of an epicyclic gear train and said annular element comprises a ring gear of said epicyclic gear train having radially inwardly projecting gear teeth adapted to be engaged by the teeth of said spur gears to thereby rotate said ring gear and said rotatable member.
 23. A machine tool comprising, a nonrotatable member having a central longitudinal axis, a rotatable load-receiving member having an opening which receives said nonrotatable member therethrough and having exposed easily accessible support means, a machining instrument detachably fixed on said support means for rotation with said rotatable member, a plurality of cutouts in one of said members defining a corresponding plurality of fluid pressure pads, a reservoir containing hydraulic fluid, first supply means for supplying and continuously flowing fluid under pressure from said reservoir through said nonrotatable member and through said plurality of pressure pads, first return means for returning said fluid from said pressure pads longitudinally through said nonrotatable member and to said reservoir, a fluid motor for rotating said rotatable member together with said machining instrument, said fluid motor having its cooperating elements provided as component parts of both said nonrotatable member and said rotatable member and in a summetrical manner about said central longitudinal axis to thereby provide substantially vibration-free rotation of said rotatable member and said machining instrument, second supply means for supplying fluid under pressure from said reservoir to said fluid motor, second return means for flowing fluid from said fluid motor into said first return means for return to said reservoir, and pressurizing means for pressurizing and supplying fluid from said reservoir to both said first supply means and said second supply means, said fluid pressure pads providing a precision fluid bearing enabling said rotatable member and said machining instrument to be rotated in a substantially frictionless manner with said fluid being circulated by said pressurizing means to provide cool operation of said members even under adverse machining conditions.
 24. A machine tool as set forth in claim 23 in which said pressurizing means comprises a single fluid pump having its inlet in fluid flow communication with said fluid in said reservoir and its outlet in fluid flow communication with both said first and second supply means to thereby supply both said fluid pressure pads and said integral fluid motor, said fluid pump comprising a load-compensating system wherein as the load exerted on said machining instrument increases the fluid pressure provided by said pump to said fluid motor increases which also increases the fluid pressure to said pressure pads thus compensating for the additional load imposed on the machining instrument.
 25. A machine tool as set forth in claim 23 in which said pressurizing means comprises a first fluid pump having its inlet in fluid flow communication with said fluid in said reservoir and its outlet in fluid flow communication with said first supply means, and a second fluid pump having its inlet in fluid flow communication with said fluid in said reservoir and its outlet in fluid flow communication with said second supply means.
 26. A machine tool as set forth in claim 23 in which said fluid motor comprises a plurality of spur gears of an epicyclic gear train supported for rotation on said nonrotatable member and a ring gear of said epicyclic gear train fixed to said rotatable member and having radially inwardly projecting gear teeth adapted to be engaged by the teeth of said spur gears to thereby rotate said ring gear and said rotatable member, and said machine tool fuRther comprising opposed recess means provided in said nonrotatable member, each recess means defining a fluid balance pad and being arranged to face an associated surface of said ring gear, said balance pads being provided with fluid under pressure and cooperating to define a precision self-adjusting axial thrust bearing for said rotatable member. 